Over the years, there have been a variety of proposals for braking systems in drive trains of the sort having a driving shaft, typically connected to a prime mover, motor or the like, and a driven shaft typically connected to a load or the like. In many instances, as, for example, in positioning aircraft control surfaces, it is highly desirable that the driven shaft be prevented from overrunning the driving shaft in either direction of rotation. In the case of use of such systems for positioning aircraft control surfaces, such overrunning may be encouraged by inertial forces, i.e., the tendency of a flap or slat to continue in motion once set in motion by a controlling motor even when the input to the drive train from the motor has been stopped by de-energizing the motor, gravitational forces as when flaps are being lowered, and aerodynamic forces generated by the passage of the control surface through the air.
Where braking systems are not employed in drive trains utilized in such environments, such forces as mentioned immediately preceding may overcome the resistance in the positioning element, usually a control motor, with the consequence that a desired control surface configuration cannot be maintained without further and continual attention by the operator, typically a pilot.
Even where brake systems are incorporated in the drive trains used in such environments, difficulties may attend their use. For example, if there is a break in the drive train between the control elements and the input shaft to the braking system, the means normally employed to engage the brake, which are typically responsive to attempts at relative movement between the input and output shafts, may become ineffective due to a total lack of resistance to movement of the input shaft.
In order to overcome this difficulty, many prior art systems have resorted to the use of normally engaged brakes which can be disengaged only upon movement of the input shaft. To assure adequate braking, relatively large springs are employed in such normally engaged braking systems and as a consequence, input torque to the input shaft must necessarily be large to disengage the heavily loaded brake. Moreover, the large springs of necessity have greater weight than would smaller springs and it is well recognized in the aircraft industry that weight is a substantial concern in the construction and operation of aircraft.
In some systems, the drive connection between the input shaft and the output shaft is not positive. Such systems have the disadvantage that when slippage between the two occurs, indication to the operator or pilot of the position of the surface being controlled is not coordinated with the actual position of such surface or with other control surfaces whose positions must be considered as well; or if compensation is made to maintain coordination of indication, additional components, all carrying a weight penalty, must be included.
The present invention is directed to overcoming one or more of the above problems.